fix: allow selecting and copying Studio Code conversation text

[sejas]

Related issues

• Fixes STU-1831

How AI was used in this PR

Used to trace why conversation text was unselectable and to pinpoint the inherited select-none on the app shell as the root cause. The diagnosis and the one-line fix were reviewed manually.

Proposed Changes

Studio Code users couldn't select or copy any text from a conversation — user prompts, assistant replies, tool output, or agent questions. The app shell intentionally marks the whole window non-selectable for a native feel (select-none on the root), and that user-select: none was cascading into the conversation.

This re-enables text selection just for the Studio Code conversation, so users can highlight and copy anything the agent says (or that they said) — e.g. to reuse a command, save a snippet, or share a reply. The rest of the app chrome stays non-selectable, as before.

Testing Instructions

1. Open Studio Code tab.
2. Send a message
3. Drag-select across the user prompt and the assistant's markdown reply
4. Observe the text should highlight and can be copied.

select-text.mp4

As a follow-up we could add copy button to copy the message in markdown text.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[nightnei]

LGTM and works as expected 👍